The processes of making particles of the prior art usually entail the mixing of liquid silicates with various compounds as further described below, heating said mixture to drive off enough water to form a hard glassy material, and subsequently grinding and screening the material into particles of suitable size. Additionally, dry silicates have been employed along with water to form the necessary hydrated silicates.
Silicate-based materials have not found general broad acceptance for the end uses described herein. This is, no doubt, due to the difficulties encountered in producing a suitably dense intermediate of a formulation which has a high expansion rate, is homogeneous, non-caking, easy to handle and easy to produce. The production methods of prior art involve drying the initial mixtures to a point where they can be ground to suitable particles. This normally involves drying the initial mass for long periods of time (from 1 to 4 hours). Such long drying times are felt necessary due to the fact that the silicates in an aqueous media form a skin on their surface during drying which tends to impede further drying to an acceptable moisture range. Attempts to overcome this problem have resulted in some cases in the addition of silicates in the dry form to lower the amount of moisture which must be removed before grinding. The use of these dry silicates, however, necessitates additional waiting periods of up to four hours to allow the dry silicates to hydrate to an expandable form, or requires the use of pressures greater than atmospheric. Additionally, when employing dry silicates as a starting point, other ingredients such as fillers, insolubilizers, etc. are mixed or mulled with the silicate, and remain as discrete particles in the final dense phase, creating less homogeneous mixtures than can be produced by the use of silicate solutions, where optimum dispersions or solutions are possible. All of these methods have serious drawbacks which impede the commercial production of these materials and tend to result in high manufacturing costs.
A number of issued patents can be noted which are of interest. U.S. Pat. No. 3,756,839 relates to the preparation of silicate-based materials which may be intumesced through the use of anhydrous silicates and insoluble powders and water by hydrating said mixture by subsequent application of heat and pressure (or steam under pressure) and subsequently compacting said hydrated mixture. Compacting may be accomplished with the heat and pressure of the hydrating step or by means of a separate press or extruder. This process utilizes raw materials in a finely divided form, and the levels of insoluble powders included are limited by the non-homogeneous nature of the process.
U.S. Pat. No. 4,203,773 relates to the preparation of expanded silicate aggregates also through the use of anhydrous silicates. Anhydrous silicate, a curing agent and an optional insolubilizer are dry mixed; water is added and the mixture is caused to hydrate at temperatures of 80.degree.-90.degree. C. at a humidity level of 90% or higher. This hydration step takes a matter of hours to complete, and the hydrated mass must subsequently be pulverized to the required size before intumescing.
U.S. Pat. No. 3,728,208 relates to intumesced silicate compounds formed through the use of anhydrous and liquid silicates, along with other ingredients which form spumiform particles having a volume of about 3 to 4 times the volume of the extruded pellets.
U.S. Pat. No. 3,765,919 relates to the manufacture of lightweight silicate-based materials through the use of liquid and anhydrous silicates, an expansion controller and a heat triggered neutralizer. The ingredients are blended and subsequently passed into an oven to dissolve the anhydrous silicate and to cause drying of the mixture. The mixture is then cooled and crushed into suitable size particles. The crushing operation produces undesirable dust, and the retention time required in the oven is between one and four hours. Long retention times along these lines require massive increases in the size or length of plant equipment and tend to severely limit production capacity.
U.S. Pat. No. 2,039,008 relates to the use of liquid silicates along with clays. The initial mixture is extruded into short cylinders and the cylinders are covered with talc to prevent them from sticking to each other. The coated cylinders are then heated to cause the silicate to puff. The addition of another compound (talc) added in a non-homogeneous fashion (as an outside coating) is undesirable, and no attempt is made to produce dense, easily handled, non-caking intermediate particles for expansion at a later time.
U.S. Pat. No. 2,117,605 relates to liquid silicates used along with other compounds to produce materials with a spumiform structure. After mixing and heating the ingredients, the resultant liquid is poured into shallow pans or onto a moving belt in an oven and dried until a hydrous crushable solid is obtained upon cooling. The material is then crushed to the desired size and this requires a grinding and sizing operation, with the undesirable production of dust.
It is accordingly one object of the present invention to produce dense, free-flowing, non-caking, non-dusting, easily handled particles which can be transported in their intermediate state to a remote location and, at the job site, treated to form the desired end product.
It is a further object of the present invention to produce relatively dense intermediate particles having a smooth outer surface, and which expand or intumesce when rapidly heated at about 400.degree.-1600.degree. F. into rigid particles of a spumiform nature, with particle volumes which are at least about five times the volume of the original particles.
It is another object of the present invention to produce dense intermediate particles without the need for long drying times, grinding, and/or the use of pressures greater than about atmospheric pressure. These and other objects will be apparent to those of skill in the art from the teachings herein.